The only zero of f′⁢(x)superscriptfnormal-′xf^{{\prime}}(x) is x=bxbx=b, where the sign changes from minus to plus as xxx increases. It means that x=bxbx=b is the searched minimum point. The difference in altitude is thus equal to the base, and the inclinationαα\alpha must be 45∘superscript4545^{\circ}.